The present invention relates to aqueous alkaline non-cyanide zinc plating baths, and to a novel brightening agent for such electroplating baths.
This invention relates to improvements in the electrodeposition of zinc from aqueous alkaline cyanide-free plating baths. The alkaline cyanide-free zinc plating baths that have been developed over the years are generally based on polymeric quaternary amines as brightening agents. U.S. Pat. No. 3,824,158 describes an aqueous alkaline zinc electroplating bath containing an epihalohydrin quaternary salt of aminated polyepichlorohydrin. U.S. Pat. No. 3,869,358 describes an aqueous alkaline zinc plating bath for electroplating bright metallic zinc deposits having dissolved therein a water soluble reaction product of an amine and an epihalohydrin containing recurring tertiary and/or quaternary amine groups. U.S. Pat. No. 3,954,575 describes an alkaline non-cyanide zinc plating bath wherein the brightener additive comprises a water soluble polymer prepared by the reaction of at least one epihalohydrin with at least one nitrogen heterocyclic compound. U.S. Pat. No. 5,435,898 describes an aqueous bath for electrodepositing zinc and zinc alloys wherein the bath contains an effective additive amount of a quaternary ammonium polymer to produce enhanced deposits. German Patent DE 198 40 019 C 1 describes a brightener for alkaline cyanide-free zinc plating comprised of a ureylene quaternary ammonium polymer.
When polymeric quaternary amines are used as brightener additives in an aqueous alkaline cyanide-free zinc plating bath, metal hydroxides on the surface of the parts to be plated cause the electrodeposit to have a cloudy, dull appearance. Accordingly, complexing agents such as salts of gluconic acid and E.D.T.A. are added to the baths to overcome the detrimental effects of the presence of metal hydroxides. While this solves the problem of cloudy, dull electrodeposits, precipitation of metals during waste treatment becomes quite difficult.
An object of the present invention is to provide an aqueous alkaline cyanide-free zinc electroplating bath that produces bright electrodeposits of zinc.
It is a further object of the present invention to provide bright, clear electrodeposits of zinc in the presence of metal hydroxides on the surface of the parts.
Another object of the present invention is to provide an aqueous alkaline cyanide-free zinc electroplating bath that produces bright, clear electrodeposits of zinc without interfering with the precipitation of metals during waste treatment.
These and other objects and advantages will be apparent from the following description.
These objects and advantages are achieved by the addition of a reducing sugar to an aqueous alkaline cyanide-free zinc electroplating bath having a polymeric quaternary amine dissolved therein. The polymeric quaternary amines of this invention are well known in the plating industry and include epihalohydrin reaction products with various amines, quaternized polyethyleneimines, and ureylene quaternary ammonium polymers. The electrodeposits achieved are bright and are produced in the presence of metal hydroxides on the surface of the parts to be plated. Moreover, the improved baths of this invention have an advantage over baths of the prior art in that they readily permit the precipitation of metals during waste treatment procedures.